1. Field of the Invention
This invention relates to ionizing radiation sensitive materials which are useful as electron beam resists and information recording media.
2. Description of the Prior Art
It is well-known that electron beam irradiation will cause crosslinking of certain polymers. An article by Herbert S. Cole et al entitled "Electron Sensitive Resists Derived from Vinylether-Maleic Anhydride Copolymers" in the IEEE Transactions on Electron Devices, July, 1975, p. 417-420 and U.S. Pat. No. 3,703,402 describes a series of such materials made of octadecylvinyl ether and maleic anhydride copolymer half esterified with, among other allyl or propargyl alcohol or hydroxyalkyl acrylate. The authors state that the most efficient radiation induced crosslinking reactions are activated through the presence of an unsaturated terminal group in the resist, and, accordingly, there is a direct association between increased sensitivity and terminal unsaturation. Their experimental results indicated that reduction or elimination of terminal unsaturation caused a drastic decrease in the sensitivity of the resist polymer, and that to require a radiation dose no greater than 5.times.10.sup.-7 C/cm.sup.2 an unsaturated half ester is required and that the unsaturation must be terminal unsaturation.
In the present invention, contrary to the teaching of Cole, it has been discovered that resist compositions equally as sensitive can be obtained with a copolymer that has the terminal unsaturation drastically reduced. Even more significantly, it has been found that the contrast of such resists improves appreciably, which feature provides a resolution capability of less than 0.5 micrometer. This increased contrast is achieved herein with resists made by reacting an alkylvinyl ether-maleic anhydride copolymer with a hydroxyalkyl acrylate such as hydroxyethyl acrylate, hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropylmethacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate or allyl or propargyl alcohol or pentaerythritol triacrylate and an N-hydroxyalkyl amide or an N-aminoalkyl amide to form the novel half-ester copolymer.